In the past, sprayable paints and adhesives frequently have been organic solvent based. The solvent is used to maintain the material in a sufficiently fluid state to permit spraying. Organic solvents were selected to achieve rapid drying. As the sprayed material dries, solvent enters the atmosphere and can be hazardous. Recently, there has been an increasing demand for two component materials in which a water born coating or adhesive material is chemically hardened or activated through the use of a separate catalyst or activator. As used hereinafter, the term "catalyst" will be used generically to describe any catalyst or activator or other type of chemical which is added to a coating material to promote a change in the material. Some types of adhesive and other types of coating materials, such as epoxy type materials, may have a relatively long pot life after mixing with a catalyst. The long pot life permits mixing the components either prior to delivery to a spray gun or internally in the spray gun. The pot life of the mixture is sufficiently long as to permit cleaning the spray gun after spraying. Other types of two component materials must be mixed externally to the spray gun, since there is not a sufficient pot life of the mixture to permit easy cleaning of the spray gun after the material is mixed or contacted with the catalyst.
In prior art spray guns for externally mixed two component materials, the coating or adhesive material is sprayed from a modified conventional spray gun. The spray gun has been modified by mounting a mechanically operated catalyst valve on the gun. The catalyst valve has been mounted towards the rear of the spray gun body where it is easily connected through linkages to be operated by the existing spray gun trigger. The linkages are adjusted to open the catalyst valve immediately prior to opening the fluid valve for the coating or adhesive material. This assures that all sprayed material will be exposed to catalyst. In one prior art spray gun, the catalyst valve was connected through a small tube to spray the catalyst at the atomized fluid at a point downstream from an air cap. In this arrangement, the catalyst was sprayed only at one side of the atomized fluid envelope. Consequently, the atomized fluid was not uniformly exposed to the catalyst. The material spaced furthest from the catalyst nozzle was not necessarily exposed to sufficient catalyst, resulting in a defective application of paint or adhesive. In an improved prior art gun, the catalyst was injected into a pattern shaping air chamber in the air cap or upstream from the air cap for mixing with the pattern shaping air. This arrangement provides superior contact between the catalyst and the atomized material immediately downstream from the spray gun nozzle. However, there have still been some problems with this arrangement. Because the valve has been located at or near the rear end of the gun body in order to connect the operating linkages to the trigger, a relatively long tube is used to deliver the catalyst from the valve to the pattern shaping air chambers. When the gun is shut off and set down, catalyst in the tube sometimes has drained into the pattern shaping air chamber. This can result in a burst of catalyst in the pattern shaping air when the spray gun is first triggered. Also, the linkages connecting the catalyst valve to the trigger have been prone to damage and misadjustment which can result in an improper timing of the opening of the catalyst valve relative to the opening of the main fluid valve.